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M30 mortar
| part_length = | width = | height = | diameter = | crew = | cartridge = | cartridge_weight = | caliber = 107 mm (4.2 in) | barrels = | action = | rate = 18 rpm max., 3 rpm sustained | velocity = | range = 770 m to 6,800 m (840 yd to 7,400 yd) | max_range = 6,800 m (7,400 yd) | feed = | sights = | breech = | recoil = | carriage = | elevation = | traverse = }} The M30 107 mm (4.2 inch Mortar) heavy mortar is an American rifled, muzzle-loading, high-angle-of-fire weapon used for long-range indirect fire support to infantry units. Design The M30 system weighs 305 kg including the complete mortar with a welded steel rotator, M24A1 base plate and M53 sight. A point of interest in the design of this mortar is the rifled barrel. A rifled barrel requires the round to be a very tight fit to the bore in order for the rifling to engage the round and impart rotation to it. But in a muzzle loading mortar, the round has to be loose enough in the bore to drop in from the front. In order to have it both ways, these rounds have an expandable ring at the base which expands into the rifling under the pressure of the explosion of the firing charge which propels the round. Additionally, imparting a spin to a round causes it to drift away from the direction of fire during flight and the longer the flight (greater range to target), the farther the drift, so the computation for setting the direction for firing at a specific target has to account for this drift. Types of rounds * HE M329A1—max range 5,650 m (6,180 yd), weight 12.3 kg (27 lb) * HE M329A2—max range 6,800 m (7,400 yd), weight 10 kg (22 lb) * HE M34A1—max range 4,620 m (5,050 yd), weight 12.2 kg (26.9 lb) There was also a sub-caliber training device that utilized blank 20 gauge shotgun shells to propel an inert training round a few hundred meters. History The M30 entered service with the US Army in 1951, replacing the previous M2 107 mm mortar.4.2 inch M30 Mortar It was adopted due to the extended range and lethality in comparison to the previous M2 107 mm mortar, although the M30, at 305 kilograms, was significantly heavier than the 151 kilogram M2. Due to this heavy weight the mortar was most often mounted in a tracked mortar carrier of the M113 family. This vehicle mounted mortar was crewed by 5 people: the track commander (mortar sergeant/gun commander), gunner, assistant gunner, loader and vehicle driver. Ground mounting of the mortar was time consuming and strenuous as a hole had to be dug for the base plate of the mortar to rest in, sandbags had to filled and placed around the base plate to stabilize it and to protect the exposed ammunition. Also this decreased the accuracy of the weapon as the recoil from firing caused the base plate to shift in the ground. This movement also made the crew have to "lay" the gun back on the aiming stakes more often, causing a temporary lack of fire while the weapon was repositioned and re-sighted back to its original reference point. References Category:Weapons of the Vietnam War Category:Anti-communist forces weapons